The present invention relates to a device for the integration of a large number of sensors that share a common data path. More particularly, the present invention relates to a digital interrogation system for use with a sensing grid system which is used to obtain data from a plurality of sensors used in connection with monitoring the flow and cure rate of a resin material.
The ability to produce a composite material having specified properties is of great importance in a variety of military, as well as commercial fields. Being able to monitor the production of these materials in order to assure the presence of the essential properties required for a specific purpose would be a significant advancement in the composite material art. Monitoring the production of resin material to make sure that it has certain, unique properties such as strength, stiffness and weight, or combinations of those properties, would enable material scientists to better develop the materials needed. Such monitoring would allow one skilled in the composite material art to successfully produce a material needed with less waste, and with the ability to identify any unfavorable properties of the composite material while it is in the production stage, instead of in the testing stage. It also allows for variations in the production process to be made in the early stages of development.
The prior art teaches the use of fiber optics for detecting damage in composite structures. Hofer, in an article entitled "Fiber Optic Damage Detection in Composite Structures," Composites, Volume 18, No. 4 (September, 1987), describes a method for inspecting a composite material for remote damage. The method described utilizes surface mounted or embedded fiber optic cables. The fiber optic cables can be drawn out to diameters comparable to that of the composite material reinforcement. Hence, the fiber optic cables can be embedded permanently in the composite without significantly influencing the overall integrity or properties of the composite material. Although the present invention may be adapted for use with the fiber optic cables described in the article, nowhere in the article is it taught that the fiber optic arrangement therein provides a means for determining resin location and cure during composite fabrication. Moreover, nowhere in the article is the grid-like system used with the present invention set forth. The fiber optic system described in the Hofer article does not possess the novel features within the scope of the present invention.
A wide variety of devices already exist for monitoring the curing process of a wide range of resin materials. Those existing devices utilize a variety of dielectric or microdielectric techniques to measure the electrical resistance or capacitance of the resin material being produced. The information obtained by those prior art techniques is then passed to a series of conventional signal conditioners, computer hardware and software. The conventional signal conditioners, computer hardware and software then interpret that information and display it in a fashion which illustrates the curing process of the resin materials.
Prior art in composite monitoring utilizes the basic, conventional dielectric and microdielectric techniques. Those techniques have been available, and have been used in the art for quite some time. Some patents illustrating the use of those well-known techniques are discussed in U.S. Pat. No. 5,210,499 to Walsh, the disclosure of which is incorporated herein.
The sensors taught in the patents discussed in U.S. Pat. No. 5,210,499 to Walsh cannot be incorporated into the composite materials to be monitored in large numbers because of the size, cost, and limited means of, attachment. Since those sensors cannot be incorporated into, the materials in large numbers, the uniformity of properties of the composite material being produced cannot be accurately monitored. Moreover, the prior art sensors, even if they could be incorporated into the composite materials in large numbers, are prohibitively expensive; therefore, an alternate monitoring apparatus and method must be considered.
Berry, U.S. Pat. No. 3,383,863, teaches a method of detecting leaks in a pond, tank and pit. Berry makes use of a grid of electrical wires wherein the resistance between different wires of the grid are measured. It appears that the grid of electrical wires in that reference need not intersect with one another as one would expect in a conventional grid configuration. Note column 2, lines 65-70. Although Berry appears to teach the specific grid-like configuration used with the present invention, nowhere does the reference suggest employing such a grid-like sensor to monitor resin flow or resin cure. Moreover, Berry makes use of an ohmmeter. The use of the monitoring apparatus of the present invention, i.e., a scanner and/or computer device, are not even remotely suggested by the teachings in Berry.
The present invention offers an apparatus and method that is convenient, because of its use of conventional, electrically conductive, sensor threads; inexpensive, because of its maximizing the use, of each sensor thread; and reliable. The sensing grid used with the present invention can be imbedded not only in the composite reinforcement, but it can be part of the bleeder, breather, and bagging materials as well. The invention provides a means for monitoring resin migration during autoclave, hot press and other prepreg composite processes. The present invention also provides a means for evaluating and monitoring thorough wet-out and cure, as well as a means for determining optimum mold and process configurations of the composite resin materials as they are being produced. Furthermore, the device can provide three-dimensional flow field information, as well as local resin flow front velocities.
The present invention makes use of, for example, the electrically conductive threads in a set grid-like configuration as disclosed in U.S. Pat. No. 5,210,499 to Walsh. The cost of performing the monitoring function is, therefore, kept to a minimum. To date, only the Walsh patent has disclosed an instrument for monitoring the cure of a wide range of resin systems using sensors that are incorporated as integral components of the composite resin structure. The present invention is directed to an improved device for utilizing a sensor system having a grid-like array of non-intersecting electrically conductive threads or other materials to serve as leads that can be connected to the instant sensor network scanner.
The present sensor network scanner overcomes the disadvantages inherent in the device disclosed in the Walsh patent. For example, the multiplexer/rapid switching system, scanner and computer system disclosed in that patent requires expensive up front costs as well as substantial additional costs in order to expand its monitoring capabilities to larger grids. In addition, the system disclosed in the Walsh '499 patent operates relatively slowly and is not practical for real time applications having large parts and sensor grids.
The present sensor scanning system, on the other hand, is a portable solid state digital scanning system whose scanning speed is accomplished much more quickly and requires much less cost than prior art systems to expand to larger parts and sensor grids. The instant invention is intended for use, as a device to interrogate a network of interconnected sensors that share a common data path. Such sensors must operate either by making or breaking a connection as a result of changes which occur in the sensor environment. The present invention provides a fast and efficient means with which to interrogate the sensor system and allows the output to be displayed visually or to be made available to a host computer.
In addition to the advantages discussed above, the sensor network scanner of the present invention operates independently of a computer but can easily be interfaced to or implemented in software on a computer. Further, due to the symmetry of the design and the modular nature of the disclosed sensor network scanner, the instant scanner can be readily expanded to include additional sensors with minimal circuit revision and at low cost.